The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Shock absorbers are typically used in conjunction with automotive suspension systems or other suspension systems to absorb unwanted vibrations that occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/drivetrain) masses of the vehicle.
In typical shock absorbers, a piston is located within a fluid chamber defined by a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the fluid chamber of the pressure tube into an upper working chamber and a lower working chamber. The piston includes compression valving that limits the flow of hydraulic fluid from the lower working chamber to the upper working chamber during a compression stroke. The piston also includes rebound valving that limits the flow of hydraulic fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. By controlling the fluid flow between the two working chambers, a pressure drop is built up between the two working chambers. Because the compression valving and the rebound valving each has the ability to limit the flow of hydraulic fluid, the shock absorber is able to produce damping forces that counteract oscillations/vibrations, which would otherwise be transmitted from the unsprung mass to the sprung mass.
Typical shock absorbers provide the same magnitude of damping force regardless of the length of a damper stroke. However, shock absorbers have been developed where the magnitude of the damping force generated by the shock absorber during smaller damper strokes is different from the magnitude of the damping force generated by the shock absorber during larger damper strokes. These multi-force shock absorbers provide a relatively small or low damping force during the normal running of the vehicle and a relatively large or high damping force during maneuvers requiring extended suspension movements. The normal running of the vehicle is accompanied by small or fine vibrations of the un-sprung mass of the vehicle and thus the need for a soft ride or low damping characteristic of the suspension system to isolate the sprung mass from these small or fine vibrations. During a turning or braking maneuver, as an example, the sprung mass of the vehicle will attempt to undergo a relatively slow and/or large vibration, which then requires a firm ride or high damping characteristic of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. Thus, these multi-force shock absorbers offer the advantage of a smooth steady state ride by eliminating the high frequency/small excitations from the sprung mass, while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing larger excitations of the sprung mass.
One such multi-force shock absorber is disclosed in U.S. Pat. No. 6,220,409, which is also assigned to Tenneco Automotive Inc. This shock absorber provides two stages of damping (hard and soft) by utilizing a stroke dependent damper assembly that is mounted to the piston rod below the main piston assembly. The stroke dependent damper assembly includes a piston that is longitudinally moveable between two rubber travel stops. These resilient travel stops act as mechanical stops for the piston when the piston reaches its travel extremes. When the piston hits one of these resilient travel stops, especially during a rebound stroke, a pressure wave can be created in the hydraulic fluid of the shock absorber that can vibrate the piston rod and cause noise.
Accordingly, there remains a need in the marketplace for stroke dependent shock absorbers with improved noise, vibration, and harshness.